A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle is equipped with a navigation function to guide a driver to a destination through a calculated route. Such a navigation system detects the position of the user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), a hard disc, or from a remote server.
Typically, the navigation system displays a map image on a monitor screen while superimposing thereon a mark representing the current location of the user. Such algorithm as A* search algorithm and its variants are generally used to search and calculate a route to a destination. A user is able to watch a map on a display of the navigation system where the map provides information such as streets, current location of the vehicle, and points of interest (POI), etc.
One of the typical functions that is considered useful in operations of a navigation system is an ability to display various icons on a map image. FIG. 1A is a schematic diagram showing an example of display of the navigation system where various icons are superimposed on a map image. As is known in the art, an icon is a small symbol on a computer, TV screen, or a display of other electronic device such as a navigation system that represents an object in a simplified manner.
As shown in FIG. 1A, in an application to the navigation system, icons typically represent with their unique business types, for example, restaurants, gas stations, parking areas, ATM machines, etc. on a map image 25. Some icons show generic category of POI (Point of Interest) such as gas station, restaurants, while other icons show a specific business or brand of POI. Since such icons give intuitive information as the type and location of the POIs or other places on the map image, various icons are now frequently used for navigation systems.
In the example of FIG. 1B, however, several icons 31A and 31B are clustered or overlapped on the map image 25 where a vehicle locator 21 on the map image 25 indicates a current vehicle position (VP). As shown, when two or more icons are clustered to the same or nearby location on the map image 25, they can be hardly distinguishable. For example, in a downtown area or a shopping area where many restaurants or stores are located in the similar locations, the icons indicating the restaurants or stores may be overlapped with one another such that each icon is not easily identifiable by the user.
Moreover, in applications of a navigation system, a user does not necessarily need to know all of the icons in an area on the map image. For instance, one may want to see only a specific category of icons such as gas station icons or old monument icons when the user is in the sightseeing trip. Thus, it is desired that such operation of displaying the icons be performed easily and intuitively for a navigation system depending on the needs and circumstances associated with the user.